7Evolution of gas exchange structuresAquatic organismsexternal systems with lots of surface area exposed to aquatic environmentTerrestrialConstantly passing water across gillsCrayfish & lobsterspaddle-like appendages that drive a current of water over their gillsFishcreates current by taking water in through mouth, passes it through slits in pharynx, flows over the gills & exits the bodymoist internal respiratory tissues with lots of surface area

9Counter current exchange systemWater carrying gas flows in one direction, blood flows in opposite directionLiving in water has both advantages & disadvantages as respiratory mediumkeep surface moistO2 concentrations in water are low, especially in warmer & saltier environmentsgills have to be very efficientventilationcounter current exchangeWhy does it work counter current? Adaptation!just keep swimming….

10How counter current exchange worksfrontback70%40%100%15%water60%30%90%counter-current5%bloodwaterblood50%70%100%50%30%5%concurrentBlood & water flow in opposite directionsmaintains diffusion gradient over whole length of gill capillarymaximizing O2 transfer from water to blood

11Why don’t land animals use gills?Gas Exchange on LandAdvantages of terrestrial lifeair has many advantages over waterhigher concentration of O2O2 & CO2 diffuse much faster through airrespiratory surfaces exposed to air do not have to be ventilated as thoroughly as gillsair is much lighter than water & therefore much easier to pumpexpend less energy moving air in & outDisadvantageskeeping large respiratory surface moist causes high water lossreduce water loss by keeping lungs internalWhy don’t land animals use gills?

12Terrestrial adaptationsTracheaeair tubes branching throughout bodygas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory systemHow is this adaptive?No longer tied to living in or near water.Can support the metabolic demand of flightCan grow to larger sizes.

13Why is this exchange with the environment RISKY?Exchange tissue: spongy texture, honeycombed with moist epitheliumLungsWhy is this exchange with the environment RISKY?Lungs, like digestive system, are an entry point into the bodylungs are not in direct contact with other parts of the bodycirculatory system transports gases between lungs & rest of body

14Alveoli Gas exchange across thin epithelium of millions of alveolitotal surface area in humans ~100 m2

15Negative pressure breathingBreathing due to changing pressures in lungsair flows from higher pressure to lower pressurepulling air instead of pushing it

19Breathing and HomeostasisATPHomeostasiskeeping the internal environment of the body balancedneed to balance O2 in and CO2 outneed to balance energy (ATP) productionExercisebreathe fasterneed more ATPbring in more O2 & remove more CO2Diseasepoor lung or heart function = breathe fasterneed to work harder to bring in O2 & remove CO2CO2O2

20Diffusion of gasesConcentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissuecapillaries in lungscapillaries in muscleO2O2O2O2CO2CO2CO2CO2bloodlungsbloodbody

22Hemoglobin Why use a carrier molecule? Reversibly binds O2O2 not soluble enough in H2O for animal needsblood alone could not provide enough O2 to animal cellshemocyanin in insects = copper (bluish/greenish)hemoglobin in vertebrates = iron (reddish)Reversibly binds O2loading O2 at lungs or gills & unloading at cellsheme groupThe low solubility of oxygen in water is a fundamental problem for animals that rely on the circulatory systems for oxygen delivery.For example, a person exercising consumes almost 2 L of O2 per minute, but at normal body temperature and air pressure, only 4.5 mL of O2 can dissolve in a liter of blood in the lungs.If 80% of the dissolved O2 were delivered to the tissues (an unrealistically high percentage), the heart would need to pump 500 L of blood per minute — a ton every 2 minutes.cooperativity

30Fetal hemoglobin (HbF)HbF has greater attraction to O2 than Hblow % O2 by time blood reaches placentafetal Hb must be able to bind O2 with greater attraction than maternal HbBoth mother and fetus share a common blood supply. In particular, the fetus's blood supply is delivered via the umbilical vein from the placenta, which is anchored to the wall of the mother's uterus. As blood courses through the mother, oxygen is delivered to capillary beds for gas exchange, and by the time blood reaches the capillaries of the placenta, its oxygen saturation has decreased considerably. In order to recover enough oxygen to sustain itself, the fetus must be able to bind oxygen with a greater affinity than the mother.Fetal hemoglobin's affinity for oxygen is substantially greater than that of adult hemoglobin. Notably, the P50 value for fetal hemoglobin (i.e., the partial pressure of oxygen at which the protein is 50% saturated; lower values indicate greater affinity) is roughly 19 mmHg, whereas adult hemoglobin has a value of approximately 26.8 mmHg. As a result, the so-called "oxygen saturation curve", which plots percent saturation vs. pO2, is left-shifted for fetal hemoglobin in comparison to the same curve in adult hemoglobin.Hydroxyurea, used also as an anti-cancer drug, is a viable treatment for sickle cell anemia, as it promotes the production of fetal hemoglobin while inhibiting sickling.What is the adaptive advantage?2 alpha & 2 gamma units